1. Field of the Invention
The present invention relates to a system for controlling ignition timing wherein knocking of an engine is detected, and ignition timing is instantly delayed in response to the detected knocking. More particularly, this invention is related to a system for controlling ignition timing wherein, when a knocking sensor is out of order, ignition timing is delayed by a predetermined value.
2. Prior Art
Knocking of an engine is a dangerous phenomenon which may destroy the engine in the worst case. Hence, in the conventional ignition system, ignition timing is retarded from the ideal (with respect to performance) to ensure that knocking will not occur. However, since it is not desirable from the viewpoint of economics of fuel consumption to delay ignition timing simply to ensure knocking does not occur, a system has been developed for controlling ignition timing wherein the occurrence of knocking is fed back to advance the timing toward the ideal to the greatest degree possible without the occurrence of knocking (for example, Japanese Patent Application Laid-Open (Kokai) No. 87537/1977).
Now, in the system for controlling ignition timing as described above, knocking is detected to feedback control the ignition timing, the ignition timing is delayed when knocking takes place, and the ignition timing is feedback controlled from engine conditions so as to advance the ignition timing to the limits of knocking when knocking does not occur. However, this system is disadvantageous in that, if a knocking sensor is out of order, the condition of knocking cannot be detected. Therefore the knocking sensor sends out a signal indicating that no knocking exists despite the fact that knocking is occurring. Thus, the ignition timeing is unusually advanced to cause a violent knocking condition in the engine. In the worst case this results in the melting of the pistons and exhaust valves, which leads to the destruction of the engine.